He used to play as a defensive midfielder in his youth for former club Étoile Carouge, but when he arrived at Arsenal, he was converted to a central defender. He occasionally filled in at full back for Arsenal and played several games in central midfield while on loan to Birmingham City. He spent time on loan at Hannover 96 in 2013 before joining Hamburg, initially on loan, later that year. According to his profile on Arsenal's website, Djourou possesses "pace, power and whole-hearted commitment" in addition to his versatility.[5]

Djourou was born in Abidjan, Côte d'Ivoire, to Ivorian parents Joachim and Angeline, and was later adopted by his father's first wife Daniele, a Swiss woman.[6] They moved to Geneva when he was 17 months old. He enrolled at the Payerne Training Center when he was 13 and then in 2002 joined local second division side Étoile Carouge as a midfielder at 15. He joined Arsenal on 1 August 2003. He was a member of the Swiss under-19 squad that reached the semi-finals of the 2004 European Championships.[7]

Djourou made his first senior start for Arsenal in a 3–1 victory against Everton in the League Cup, having made his first appearance after 89 minutes of the corresponding match in the previous round against Manchester City on 27 October 2004. He made his full Premiership debut for Arsenal in the 7–0 victory over Middlesbrough on 14 January 2006, playing at centre-back with Philippe Senderos. Djourou started Arsenal's FA Cup fourth round clash with Bolton Wanderers as part of a makeshift defence, a game in which Arsenal lost 1–0. He had also played in the third round clash with Cardiff City.

In February 2006, Djourou played in the league games against West Ham United, Birmingham City and Bolton Wanderers. In April 2006 he came on as a substitute against Aston Villa in Arsenal's 5–0 victory, replacing the injured Emmanuel Eboué. He started April's premiership game against Portsmouth, a game which also saw the comeback of Sol Campbell. During this season, several Italian clubs (including Juventus) scouted Djourou in Arsenal's reserve matches (his contract was to expire at the end of the 2006–07 season), but after the end of the World Cup, he signed a six-year contract extension with Arsenal.

On 10 August 2007, he signed for Birmingham City on loan for five months.[8] He made his debut two days later against the previous season's FA Cup and League Cup winners Chelsea. This was a closely fought contest in which Chelsea ran out eventual 3–2 winners, in which Djourou cleared off the line from Frank Lampard to keep Birmingham City in the game.[9]

In May 2008, Djourou stated that he would be willing to partner Cesc Fàbregas in midfield after the departure of Mathieu Flamini to A.C. Milan. Instead, he played in the centre of defence as first choice backup following the departure of fellow Swiss defender Philippe Senderos to A.C. Milan on a season-long loan. In September, Djourou signed a new long-term contract.[12]

After Touré's departure to Manchester City, Djourou had a chance to break into the starting eleven. However, on 11 April 2009, in a league match against Wigan Athletic, Djourou suffered a knee injury which later required surgery. In September 2009, his club estimated a recovery period of six to eight months; Arsène Wenger stated: "He will have to be patient this season."[13]

In March 2010, Djourou appeared on Arsenal TV Online's 'Arsenal Live' programme. He announced that he was getting closer to a return: "I am nearly at the end. It has been a long road for me and I am really looking forward to being back on the field." He made his return from injury as a second-half substitute in the 4–0 win over Fulham in Arsenal's final game of the season. Djourou replaced the injured Mikaël Silvestre and this was his only appearance in the 2009–10 campaign.

Due to Thomas Vermaelen's injury at the beginning of the 2010–11 campaign, Djourou received more opportunities to play. Wenger admitted that he rotates the Swiss international because he missed an entire year and does not want to lose him.[14] Djourou became Arsenal's first-choice centre-back, playing in all eight games in January 2011, during which time Arsenal conceded no Premier League goals. He scored his first goal for Arsenal on 5 February, in the third minute of a 4–4 draw against Newcastle United at St. James' Park. On 27 February 2011, Djourou started and played the full 90 minutes alongside Laurent Koscielny against Birmingham City in the 2011 Football League Cup Final held at Wembley Stadium in a 2–1 defeat.

On 12 March, while playing in the quarter finals of the FA Cup away to Manchester United at Old Trafford, Djourou suffered a suspected dislocated shoulder in a collision with teammate Bacary Sagna. Djourou was carried from the field and Wenger later confirmed that he would be unavailable for the remainder of the 2010–11 season. This came as a major blow to Arsenal's title challenge, up until then having not lost a Premier League game with him on the field. As well as that Djourou had played a major part in defence in cover of the injured Vermaelen. Djourou recovered more quickly than expected, returning to play the whole of the 1–1 draw with Liverpool at the Emirates Stadium on 17 April, playing alongside Koscielny, and the North London Derby three days later. On 24 April, against Bolton Wanderers at the Reebok Stadium, he conceded a penalty (missed by Kevin Davies) in a 2–1 defeat which effectively ended Arsenal's title hopes. At the end of the 2010–11 season, he played in a total of 37 matches for the Gunners in all competitions. On 28 August 2011 Djourou played in the centre of a young Arsenal seriously weakened by injuries for a match against Manchester United at Old Trafford. Arsenal lost 8–2, in what was their heaviest defeat since 1896, a 115-year record.[15] Three days later Arsenal announced the signing of experienced German defender Per Mertesacker from Werder Bremen, and Djourou's first team opportunities became more limited. In February 2012, Djourou signed a three-year contract extension until summer 2015. During the 2011–12 season, he started 19 times for Arsenal and made 8 substitute appearances.

On 3 January 2013, Djourou confirmed that he was set to move to Bundesliga club Hannover on loan until the end of the season, with no option to buy included in the deal. He said, "I joined the club who wanted me the most. At my age, the priority is to play regularly. To do this, I did not hesitate to refuse offers with the most exclusive clubs who made important financial efforts."[16]

On 1 July 2013, Djourou undertook a medical before signing for Bundesliga side Hamburger SV on loan for a season. It was reported that this time, the deal did include an option to buy. He said: "I'm very happy now that everything is sorted. HSV are a big club, with a lot of quality and great fans. I am convinced that this is the right step for my career."[17]

In April 2014, Hamburg confirmed that they had activated the buying clause and signed Djourou on a permanent deal.[18]

He made his senior Switzerland international debut against Scotland on 1 March 2006, coming on as a substitute and again playing alongside Philippe Senderos. Djourou was called up to the Switzerland 2006 FIFA World Cup squad, despite not playing in the qualifiers. Although third choice central defender behind Philippe Senderos, then of Arsenal, and Patrick Müller, then of Lyon, he started Switzerland's round 16 game against Ukraine. Injury, however, led him to be substituted in the first half. Later that year, he made two appearances during Switzerland's qualification campaign for the UEFA U21 Championship, but did not appear for the Swiss U21 squad since. After missing nearly the entire season for Arsenal in 2009–10, he was left out of the Swiss squad for the 2010 World Cup held in South Africa. In June 2011, with Switzerland 2–0 up against England in a Euro 2012 qualifier, Djourou fouled Arsenal teammate Jack Wilshere to concede a penalty, allowing England to pull a goal back although the match ended in a 2–2 draw at the Wembley Stadium.[19]

He scored his first goal for Switzerland, finding the net in a 4–3 friendly loss against Japan in 2007. He scored his second international goal against San Marino, converting a penalty kick after Fabian Schär had been fouled in the box for Switzerland's in a 7–0 win.